The invention relates to the field of spacecraft. More particularly, the present invention relates to orbiter and booster spacecraft.
In the beginning of the space program performance was an absolute objective. From the earliest days, however, the cost of launching payloads into space has been perceived as high. Failures were to be avoided or minimized from both a national and geopolitical perspective. The cost of launching current or proposed systems, while important, was not the driving force in designing, producing and operating early space launch systems. As such systems evolved, cost considerations seemingly became more important, particularly with the entrance of competing European and Asian launch vehicles. Consequently, a new mandate of cost reduction has in the past decade or so dominated decisions concerning any new or modified space launch system. Modernly, space system designers seek major cost reductions.
There are several ways to reduce costs of space systems, but not all cost reduction plans are possible. For example, the cost of placing a pound of payload in earth orbit has dramatically decreased due to the development of larger and thus more capable launch vehicles. The larger vehicles have an increased cost per launch than ballistic missile type antecedent space systems, but place much larger payloads in orbit. Accordingly, the cost per pound measure, that is a measure of the relative cost of launch systems, has substantially decreased even though the larger vehicles have a higher cost per launch. Another way to reduce cost is to recover all or part of a launch vehicle for relaunch after any repairs, replacements or refurbishments have been made. A prime example is the Space Transportation System using the Shuttle as the major reusable space system. Even with reuse or partial reuse, the cost of launch operations is deemed to be unacceptably high to many in the space community. So the cost reduction mandate has continued. Main proponents of cost reduction adhere to the philosophy that cost is high because of agency or bureaucratic management layering. Other system planners proclaim that technological breakthroughs will make the design and production process less costly. Together, these assertions claim that doing business a new way will make things cheaper. Many such cost reduction plans are simply not possible or highly unlikely. Another cost reduction candidate takes the reuse concept one step further by proposing a fully reusable vehicle. Candidate designs cover a host of concepts centered on multiple or single stage vehicles. A large number of private and government funded studies have been undertaken over the past decade aimed at supplanting the current Shuttle system with various designs that embrace the low cost mandate. In these studies, low cost is achieved by advancing the state of technology often in an overly optimistic and risky manner or by applying unrealistic cost reduction assumptions to the study of cost estimates.
Single stage to orbit designs offer good examples of technological risk because projected payload weight to orbit is extremely difficult to achieve even with very large vehicles. The slightest unanticipated weight increase in any of the many complex subsystems directly decreases payload weight capability. To achieve the relatively low structure weights, required to ensure substantial payloads, untested exotic materials and advanced propulsion devices are employed in study designs. Advanced materials have also been incorporated in various multiple stage study designs, increasing the concomitant risk of not achieving design goals and of not living up to the low cost mandate.
Another way of meeting low cost goals has been the use of commonality within subsystems or within stage designs. The concept of commonality refers to use of the same part, component, or subsystem from one design to a different application. The concept is not new and has been implemented in aircraft and selected space systems. A prime example would be a propulsion system where the cost of engine development is saved when a particular engine is used in a subsequent design application. For example, the second and third stages of the Apollo launch vehicle used the same engine. Different launch vehicles have also used the same engine. Aircraft exhibit a similar history. In certain design studies on Shuttle replacement, commonality has been incorporated in the basic structure and stage tankage as well as the propulsion system.
Lower costs will usually result when such commonality can be implemented. However, commonality fails to bring about dramatic cost savings, when applied to a multiple stage launch vehicle, because each stage must be separately designed, tested and qualified, all of which represents a huge proportion of development cost. Accordingly, when studies have asserted that a two stage vehicle has the same design for each stage or similar designs, a thorough examination of the detailed weights reveals that, in fact, the stages may only be similar, and not exactly common to each other. For example, even when outside diameters of a few tank sections may be exactly the same, the stage will have different propellant capacities signifying the inherent desire of engineering designers to maximize performance. The result will be weights that differ for tanks and related structure thus failing to achieve complete commonality.
None of the known studies over the years have adopted complete commonality of both stages of a two stage launch vehicle as a driving force for cost reduction. The reasons are not obvious although the concept is relatively obvious. Designers invariably use performance optimization as a primary design objective. The physics of space flight require the use of larger lower stages and smaller upper stages failing to have commonality between the two stages. Where commonality has been applied, commonality has been applied piece meal with differing engines, tank sections or electronics, resulting, in fact, in a lack of substantial true commonality. True substantial commonality would result in only one cost of developing a system.
It appears that launch costs can be lowered through the use of a two stage vehicle where each stage is exactly the same in terms of design, development, test, qualification, production and operation. In essence, only one stage of the vehicle need be developed, only one engine and only one set of electronics, basically saving the cost of a second stage development. Production cost will be dramatically reduced because vehicles will reap the benefit of doubled quantity with economy of production run. Launch operations will be simplified because only one type of stage will need to go through the checkout procedure and subsequent refurbishment after landing. The disadvantage to the commonality design approach is that the stage must be somewhat over designed to perform both the booster and orbiter functions. However, the marginal development costs of a somewhat more capable stage is dwarfed by the savings of not having to develop and qualify another stage.
Hence, it is desirable to have a space system that offers maximum commonality to achieve cost reduction. In the case of a space system having a reusable return flight mission vehicle that is launched under propellant thrust and returns to earth through flight, such as the Shuttle, booster stages, such as the external tank and solid rocket booster, are used to aid launching the vehicle into space. The solid rocket boosters may be retrieved for later reuse. A more recent design of a reusable return flight mission vehicle having no external booster is the X33. Such a system pays a high price for combining the payload and required propellant into a single space vehicle. The resulting payload capacity is disadvantageously limited probably rendering the X33 impracticable. In one of the original proposals for the space shuttle, a design using a reusable winged booster including flight surfaces for unmanned return flights back to earth under aerodynamic flight was suggested. But again, due to the difference in mission requirements, this original launch booster design was substantially different from the Shuttle orbiter vehicle. Due to perceived differences in mission requirements, designers have failed to offer substantial commonality between the reusable return flight booster and orbiter vehicles. That is, engineers have an inherent tendency to design the best performing booster and best performing orbiter each having differing mission requirements resulting in differing designs fundamentally lacking maximum commonality. True substantial commonality has not been achieved in reusable return flight space vehicles. For 40 years there has been a strong long felt, but unsatisfied, need for inherent cost reduction, but true commonality has not been applied between boosters and orbiters because of inherent differing performance requirements coupled with inherent goals to design the best performing vehicles. These and other disadvantages are solved or reduced using the invention.
An object of the invention is to provide commonality between reusable return flight boosters and orbiters.
Another object of the invention is to provide commonality between reusable return flight boosters and orbiters having identical payload bays into which is respectively placed differing payloads.
Still another object of the invention is to provide commonality between reusable return flight boosters and orbiters having identical payload bays into which is respectively placed a propellant payload and a mission payload.
Yet another object of the invention is to provide commonality between reusable return flight boosters and orbiters having identical payload bays into which is respectively placed a propellant payload and a mission payload such that the booster and orbiters are identical spacecraft vehicles but with preferably differing payloads.
Still a further object of the invention is to provide maximum commonality between two reusable return flight space vehicles having identical payload bays into which is respectively disposed a propellant payload and a mission payload such that the two are identical spacecraft vehicles but with preferably differing payloads performing differing missions.
The invention is directed to a reusable spacecraft system having two substantially identically reusable return flight space vehicles forming a Janus type reusable spacecraft system of which one of the vehicles is conveniently referred to as a booster vehicle and the other as an orbiter vehicle. Such references suggest the type missions that the respective vehicles will have during a space mission. Both vehicles include a substantially similar payload bay into which is preferably placed differing payloads depending on mission requirements. The invention effectively equates booster propellant as a mission payload disposed in a mission payload type payload bay. In the preferred form, a propellant payload is disposed in the payload bay of the booster vehicle and a non-propellant mission payload is disposed in the payload bay of the orbiter vehicle. As such, the two vehicles possess maximum desired commonality for reduced costs of development, production, testing, launch, refurbishment, and relaunching, and possess flight surfaces for flight returns to earth for subsequent reuse. These and other advantages will become more apparent from the following detailed description of the preferred embodiment.